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تسجيل مستخدم جديدTowards a Solution for the Ca II Triplet Puzzle : Results from Dwarf Elliptical Galaxies
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We present new estimates of ages and metallicities, based on FORS/VLT optical (4400-5500A) spectroscopy, of 16 dwarf elliptical galaxies (dEs) in the Fornax Cluster and in Southern Groups. These dEs are more metal-rich and younger than previous estimates based on narrow-band photometry and low-resolution spectroscopy. For our sample we find a mean metallicity [Z/H] = -0.33 dex and mean age 3.5 Gyr, consistent with similar samples of dEs in other environments (Local Group, Virgo). Three dEs in our sample show emission lines and very young ages. This suggests that some dEs formed stars until a very recent epoch and were self-enriched by a long star formation history. Previous observations of large near-infrared (~8500A) Ca II absorption strengths in these dEs are in good agreement with the new metallicity estimates, solving part of the so-called Calcium puzzle.
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minosity) dependence from the equivalent width (EW) of the lines before converting them into metallicities. The working empirical procedure used for decades is to use the relative magnitude with respect to the horizontal branch level. Aims. The V filter is broadly adopted as the reference magnitude, although a few works have used different filters (I and Ks, for example). In this work we investigate the dependence of the CaT calibration using griz filters from the DECam and the GMOS, G from Gaia, BVI filters from the MCPS, YJKs filters from VIRCAM. We use as a reference FORS2 V filter used in the original analysis of the sample. Methods. Red giant stars from clusters with known metallicity and available CaT equivalent widths are used as reference. Public photometric catalogues are taken from SMASH DR2, VMC, Gaia, MCPS surveys plus VISCACHA-GMOS data, for a selection of Small Magellanic Cloud clusters. The slopes are fitted using two and three lines to be applicable to most of the metallicity scales. Results. The magnitude dependence of the CaT EWs is well described by a linear relation using any filter analysed in this work. The slope increases with wavelength of the filters. The zero point (a.k.a. reduced equivalent width), that is the metallicity indicator, remains the same. Conclusions. If the same line profile function is used with the same bandpasses and continuum regions, and the total EW comes from the same number of lines (2 or 3), then the reduced EW is the same regardless the filter used. Therefore, any filter can be used to convert the CaT equivalent widths into metallicity for a given CaT calibration.
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